Well no one worshipping the chaos gods wouldn't make them go away as long as the emotion s that form them exist so will they, but without outright worship they'd propably decline to a level more like the lesser gods making chaos as a whole less dangerous. (and non sentient)
each chaos god seems to have been raised from the lesser gods (blown out of proportion) due to a specific event in the past. most is only hinted upon the only we know for sure is slaanesh. Without worship they would've eventually have declined and a balance would've been re-established. Worship counteracts this.
But the gods of chaos are really not interested in the material world they're interested in the warp, but since each one sees his brothers grabbing for mortal souls he does it to. Since he sees his brother's champions slaying in their name he wants his champions to do the same.
You cant say chaos is good, no more than you can say its evil its simply a force of nature. It becomes evil when mortals chose to interfere with it. Since when they do they are setting the scales into motion, upsetting the balance.
I could be wrong but i think the beings of the warp is incapable of creative thinking of their own. Everything they do is a reflection of something the mortals do, every idea is a rehash of something they learned from mortals. Take the fact that they command Abbadon to launch black crusades. Who do you think gave them that bright idea?